1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image using developer, and a developing unit incorporated in the image forming apparatus for containing the developer.
2. Description of the Related Art
An image forming apparatus for forming an image using developer including, for example, toner forms an electrostatic latent image on a photoconductive drum as an image carrier, develops the static image in a developing unit, transfers the obtained toner image onto a paper sheet in a transfer unit, and fixes the image on the paper sheet in a fixing unit.
There is a known image forming apparatus, which has a cleaning unit to remove toner remaining on the photoconductive drum after transfer of a toner image onto the paper sheet, and reuses the collected toner (hereinafter called recycled toner).
For example, there is a toner recycling mechanism, which feeds recycled toner collected by a collecting mixer provided in a cleaning unit by means of a coupling mixer connected with the cleaning unit and developing unit, and returns the toner directly to the developing unit.
In this case, the collected recycled toner is always supplied to the developing unit while the collecting mixer and coupling mixer are operating.
The recycled toner for reuse includes toner particles peeled off partially a peculiar external additive adhered with an external additive peeled off from another toner, or mixed with paper dust. The paper dust adheres to a paper sheet as a transfer medium, and includes a long pulp fiber or cellulose fiber. Thus, when the recycled toner is put in a developing unit, the paper dust put in together with the toner is fed to a developing position and causes stained development. If the paper dust is clogged in developer blades controlling the amount of developer when the developer is supplied from a developing unit to a photoconductor, the developer is not evenly supplied to the photoconductor.